Electrical relay employing liquid metal in a capillary tube that is wet by the liquid metal



May 3, 1966 Filed Sept. 24, 1965 J E. LINDBERG, JR 3,249,722

ELECTRICAL RELAY EMPLOYING LIQUID METAL IN A CAPILLARY TUBE THAT IS WET BY THE LIQUID METAL 2 Sheets-Sheet l INVENTOR.

Joy/v L/NDBERG, Je.

May 3, 1966 J. E. LINDBERG, JR 3,249,722

ELECTRICAL RELAY EMPLOYING LIQUID METAL IN A CAPILLARY TUBE THAT IS WET BY THE LIQUID METAL Filed Sept. 24, 1965 2 Sheets-Sheet 2 JNVENToR. ./o//A/ LC. L1A/0eme, JK.

BWM

United States Patent() ELECTRICAL RELAX EMPLOYING LIQUID MET- AL IN A CAPILLARY TUBE THAT IS WET BY THE LIQUID METAL .lohn E. Lindberg, Jr., Alamo, Calif. (1211 Upper Happy Valley Road, Lafayette, Calif.) Filed Sept. 24, 1963, Ser. No. 311,616 14 Claims. (Cl. 200-122) This invention relates to improvements in electrical relays. This application is a continuation-in-part of application Serial No. 99,624, led March 30, 1961, now abandoned.

The electrical relay of this invention is characterized by novel actuation means, comprising -a'liquid metal moved by a change in the internal pressure of a closed container, they pressure increase being obtained from energy supplied by an actuating signal. More specifically, the pressure increase is produced by heating or cooling a suitable heat-dissociable solid material that lies within the container. The increase (or decrease) of pressure acts to displace the liquid metal so that it bridges a gap between two conductors and acts as a switch means for opening or closing electrical contacts. In other words, the pressure of gas liberated from heatdissociable solid material moves a suitably constrained mass of liquid metal so that it makes or breaks electrical contacts. v

One liquid metal capable of use in the invention is mercury, which is` liquid over a wide range of temperatures, incl-uding room temperature. However, for some applications metals with somewhat higher melting points (for example, gallium, Woods metal, and indium) may be used.

An important object of this invention is to provide an electrical relay of exceptionally small size which is able to give dependable operation under a wide variety of environmental conditions.

Another object of the invention is to provide a relay which can operate at very high temperatures, far beyond those at which present relays can function reliably.

A further object of the invention is to provide a relay which operates satisfactorily despite enormous changes in external pressure.

Another object of the invention is to provide a relay which is singularly unalfected by lmechanical vibration, thereby solving a problem that has heretofore plagued relay designers.

Still another object is to provide a relay that neither is affected by external magnetic fields, nor produces any signiiicant magnetic fields of its own that may interfere with adjacent electrical circuits.

Yet another object is to provide a time-delay relay in which the delay time can easily be adjusted and is continuously variable over the adjustment range.

With liquid metals that are to be moved by a gas under pressure, there is a serious problem of preventing the gas from moving through or around the liquid metal, thereby -breaking the column of liquid metal or dispers-ing it or changing its operating conditions, and it is also an object of this invention to solve this problem.

Other objects and advantages will appear from the following description of several preferred embodiments of this invention.

In the drawings:

FIG. 1 is an enlarged view in elevation and in section of a relay embodying the principles of this invention and shown in open position.

FIG. 2 is a similar view of the relay of FIG. 1, shown in closed position.-

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FIG. 3 is a similar view of a modied form of relay also embodying this invention and shown in its close position.

FIG. 4 is a similar view of the relay of FIG. 3 shown in its open position.

FIG. 5 is a similar view of another modied form of the invention, namely a relay having two normally open and one normally closed set of contacts.

FIG. 6 is a similar view of the relay of FIG. 5 shown with its normally open contacts closed and with its nor-- mally closed contacts open.

FIG. 7 is a similar view of yet another form of relay of this invention.

FIG. 8 is a fragmentary view in elevation and in section of a portion of still another modified form of relay of this invention.

This invention depends for its operation upon the use of certain solid materials that take up or evolve large quantities of gas subjected to heating or cooling. When one, or a mixture of several, of these materials is placed in a closed container, provided if necessary with a suitable supply of gas, the application of heat to the material will cause it to take up or release gas. The change in the amount of gas held in the solid material -results in a change in pressure in the closed container. Thus, the material converts changes in temperature to changes in pressure; that is, it is a temperature-to-pressure transducer. I shall hereafter use the term transducing agent when referring to such a gas-evolving solid material, A

though it may also be termed a gas-transfer agent.

Class I transducing agents are those which are stable at normal temperatures but decompose when heated above a certain triggering temperature and then liberate or emit large quantities of gas. For Class I materials, this reaction is irreversible; that is, once the material has been triggered and has released its gas, it will not readily recombine with the gas to form the original compound. Class I materials often are called blowing agents. Typical blowing agents are (l) Celogen (p,p oXybis (benzene sulfonyl hydrazide)), which decomposes between 151 C. and 156 C., liberating about 110 cc. of gas, mostly nitrogen, per gram of material, and (2) Unicel ND (dinitrosopentamethylenetetramine), which releases 116 cc. of gas, also mostly nitrogen, per gram of material, when heated to between C. and 190 C.

Class II transducing agents are those that (l) eX- hibit reversible behavior with regard to taking upy and releasing gas and (2) at low temperatures retain gas,'

but release it when heated. `Upon cooling they again take up the gas and tend to return to their original state. Among the materials of Class II are the alkaline and alkaline earth hydrides, the hydrides of certain other metals, and slome borohydrides. As I shall point out later, hydrogen is an especially useful gas when applied to this invention. It combines with or dissolves in the following Class II materials: lithium, sodium, potassium, rubidium, cesium, francium, calcium, strontium, barium, radium, scandium, yttrium, the rare earth metals (atomic numbers 57 through 71), the actinide metals (atomic numbers 89 through 103), titanium, zirconium, hafnium, vanadium, niobium, tantalum, palladium (at temperatures above 300 C.) and alloys between metals of this group. The hydrides of the alkali and alkaline earth metals are stoiehiometric; in the other hydrides listed, hydrogen forms a solution in the metal rather than a stoichiometric compound. The capacities of Class 1I materials for taking up and releasing gas vary widely from one element to another, as do their responses to certain temperatures; for example, titanium absorbs 335 cc. of hydrogen per gram at 600 C. while vanadium absorbs 10 cc. per gram ,at the same temperature.

The materials of Class III also take up and release gas reversibly, but in contrast to Class II transducing agents, they tend to take up gas when heated and release it again when cooled. Among the materials of Class III are copper, silver, molybdenum, tungsten, chromium (above 300 C.), aluminum manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, and platinum. Hydrogen reacts with or dissolves in all of these materials, which, as a rule, take up and release less hydrogen than Class II materials, given equal weights of both. Nickel, a typical metal of this type, absorbs about 5 cc. of hydrogen per gram at 600 C. Class III also includes a few oxides, of which those of silver and palladium are examples of truly reversible oxides.

The basic structure and operation of this invention is as follows: A closed container has a capillary tube of metal that is insoluble in and wet by the liquid metal to be used. The tube contains a drop of the liquid metal and provides at some point a gap between two conductors. A suitable transducing agent, which may be one or a mixture of several of the above-mentioned materials chosen to produce a desired response, along with a suitable supply of gas, if necessary, is confined in communication with one end only of the capillary tube. An increase in the internal pressure on one side of the liquid metal causes the liquid metal to move away from that side. Thus, when the transducing agent within the container is heated or cooled, the movable drop of metal is displaced, and the displacement is used to connect or disconnect the electrical conductors or contacts. The broad term relay is applicable to devices utilizing the principles of this invention.

Materials of all three classes of transducing agents find application in this invention, different embodiments of the invention employing the different characteristics exhibited by the various classes of materials. With the irreversible blowing agents, there is only one actuation, but this is often desirable, for use in one-time devices.

The relay 9 of FIGS. 1 and 2 includes a non-porous tube 10 of electrically insulating material. At one end 11 a transducing agent 12 (e.g., powdered titanium hydride) is kept in place by a porous plug 13. A iilament 14 may be imbedded in the agent 12, with leads 15 and 16 brought through the wall of the tube 10 through gastight seals 17 and 18. A metal tube 20 its snugly in the bore 21 of the tube 10, so that no gas can pass between the tube 20 and the bore 21. A metal cap 22 with an integral contact sleeve 23 seals the opposite end 24 of the tube 10. A drop 25 of mercury (or other suitable liquid or molten metal) is held inside of the tube 20 by capillary attraction. If mercury is used, the tube 20 is made of a metal which is wet by the mercury, such as clean iron or nickel. With indium the tube 20 may be copper or nickel, metals which are wet by indium.

The tube 20 is connected to one side of an E.M.F. 26 by a lead 27, which is brought out through a gas-tight seal 2,8 in the tube 10, while the cap 22 is connected to the other side of the 26 by a lead 30 that passes through a load 31. The cap 22 is a metal not wet by the liquid metal 25; e.g., where mercury is used, the cap 22 may be molybdenum. When current is passed through the filament 14, the transducing agent 12 liberates gas, and the gas pressure forces the mercury drop 25 over into a chamber portion 32, thereby bridging a gap 33 between the contact sleeve 23 and the tube 20 and completing the circuit between these two elements. This condition is shown in FIG. 2. When the current through 3 and 4. It is essentially similar to the relay 9 except for the normal resting place of its drop 41 of mercury or other liquid metal. In this case two tubes 42 and 43 of metal wet by mercury are separated by a gap 44 which lies between the tube 42 and a contact member 45 that is connected electrically to the tube 43. In its normal (relay-unactuated) position, the drop 41 of mercury inside the tubes 42 and 43 bridges the gap 44 and so completes an electrical connection between leads 46 and 47. When a transducing agent 50 is heated by a filament 51, it outgasses, and the drop 41 of mercury is forced over into a chamber 52, breaking the electrical connection between the tubes 42 and 43, as shown in FIG. 4. The tube 43 is electrically connected to a cap 54, which is made of metal not wet by mercury, so that a drop will remain close to the gap. Thus, when the agent 50 ingasses again, the pressure in the chamber 52 exceeds that in the remainder of the container 53, so that pressure diiierential and the capillary attraction of the tubes 42 and 43 for mercury cause the drop 41 to return to its normal position bridging the gap 44, again closing the circuit between the leads 46 and 47, as shown in FIG. 3.

The tube 20 in FIGS. l and 2 and the tube 53 in FIGS. 3 and 4 may be made of glass, ceramic, quartz, plastic, or any other vsuitable non-porous, insulating material, care being taken to avoid reaction between it and the agent 12 or 50. The tubes 20, 42, and 44 need not be made separately and inserted into the tube 10 or 53; rather they may be metallic films deposited in a suitable manner on the inner surface of the tube 10, taking care that they extend only over the proper areas. Similarly, the concave portion of the contact 21 or 45 may also be a metallic film connected electrically to a suitable metal cap which seals the end 13 of the tube 10 or the corresponding end of the tube 53.

FIGS. 5 and 6 show a modified form of relay 60 containing three separate switches, two normally open and one normally closed, all operated simultaneously by the same supply of transducing agent 61 and in the one tube 62. Each section of the relay in FIGS. 5 and 6 is like that of its type in FIG. l or 2, having tubes 63 and 64 separated by a gap 65, tubes 66 and 67 separated by a gap 68, and tubes 69 and 70 and a cap or contact member 71, the tubes 69 and 70 being separated by a gap 72. The tubes 64 and 66 are separated from each other by a porous plug 73, and the tubes 67 and 70 are separated by a porous plug 74. When the agent 61 outgasses, a first drop 75 of mercury is forced into a chamber 76, bridging the gap 65. The resulting increase of pressure in the chamber 76 is transmitted through the porous plug 73 and forces a second drop 77 of mercury into a chamber 78, bridging the gap 72. The resulting increase of pressure in the chamber 78 is transmitted through the porous plug 74 and forces a third drop 80 of mercury into a chamber 81, breaking the connection across the gap 72, as shown in FIG. 6. When the agent 61 ingasses again, the mercury drops 75, 77, and 80 return to their normal positions, as shown in FIG. 5, under the inuence of the pressures in the chambers 76, 78, and S1 and the capillary attraction of the various wettable metal tubes for the drops of mercury.

Clearly an indefinite number of switches could be operated together in an end-to-end arrangement like that in FIGS. 5 and 6. The types of switches incorporated may be varied to give unlimited combinations of normally open and normally closed contacts. The tube 62 of the relay 60 in FIGS. 5 and 6 may be straight, as shown, or may be bent, coiled, or formed into any shape convenient for the application.

FIG. 7 shows another modified form of relay 100 having a tube 101, made of metal which is wetby mercury (or by whatever molten metal is used) and which does not react with the transducing agent or gas liberated therefrom. Inside the tube 101 at its closed end is a quantity of transducing agent 102, kept in place by a porous plug 103. Imbedded in the agent 102 is a wire filament 104 with leads 105 and 106 brought through the wall of the tube 101 through gas-tight, insulated seals 107 and 10S. The open end 110 of the tube 101 -is sealed gas-tight into one end of a nonporous insulating tube 111. Into the other end of the -tube 111 is sealed gas-tight a contact cap 112 yof metal which is not wet by mercury. Inside the tube 101 between the porous plug 103 and the open end 110 is placed a drop 113 of mercury (or other suitable liquid or molten metal). The operation of this relay 100 is quite like that of the relay of FIG. l; the relay 100 is, however, somewhat simpler in design and construction. When the relay 100 is operated, the drop 113 of mercury makes an electrical connection between the tube 101 and the contact cap 112, completing an external circuit between leads 114 and 115 through an 116 and a load 117.

A suitable metal for the tube 101 is nickel, fo'r example. The filament 104 may be made of tungsten or molybdenum. A suitable material for the contact cap 112 is molybdenum.

In order for capillary attraction to be effective in holding the mercury drop in place, the tube (20 in FIGS. 1 and 2, 42 and 43 in FIGS. 3 and 4, 101 in FIG. 7) in which the mercury normally rests is of rather small diameter: of the order of 1,40 of an inch or less. This fact makes the overall size of the relay quite small and makes it ladmirably suitable for application to Subminiature and microminiature electrical equipment.

Depending upon the internal pressure at which the relay is designed to operate, relatively high currents may be handled by a relay of this design. The current-handling capacity `of such a relay is limited by the boiling point of the metal used as the molten drop (and, of course, by the melting points of the material components in the relay). This boiling point can be raised by increasing the internal pressure in the relay or by the choice of the metal or alloy used. Iny addition, the current-carrying capacity can be increased by supplying etlicient cooling to the relay structure. Since the contacting material is a molten metal and since the interior of the relay contains an easily controlled atmosphere (hydrogen and possibly an inert or noble gas), no problems of contact burning at high currents are encountered. All of these factors being considered, relays kof this design can handle several amperes of current.

On the other hand, since so little work has to be done to move the mercury drop, these relays can be made to operate on quite small power; in the order of 100 milli- Watts or less.

Relays of thetypesshown in FIGS. 1-7, may be grouped together side-by-side in bundles to form complex switching modules. These may be used in computer applications in which conventional relays have heretofore been considered impractical because of their excessive bulk. .These extremely small relays might remove many of the objections to using relays as switching elements in computers.

The wettable metal that contains the drop of molten metal should not be appreciably soluble in the molten metal. For example, in the case of mercury, neither gold nor copper would be satisfactory, for, although both are easily Wet by mercury, both are fairly soluble in mercury. However, both nickel and iron, when clean, are easily wet by mercury and are not soluble in it.

Having the capillary tube of metal wet by the liquid metal causes the drop to adhere to the tube wall and prevents transfer of gas from the gas pressure generator around the drop; While this feature applies to gas generator systems without solid transducing agents, drop adherence enables the large pressure differential between oppositevsides of the drop and the rapid response rates and wide range of energy inputs resulting from heating a hydride. The invention further avoids changes in calibrations due to transfer of gas past the metal drop. Rapid spatial acceleration of the relay (as in an airplane) will not damage my relay, but it would damage one where gas could pass around the drop and break up or relocate the drop. The cap is of non-wetting metal to retract the drop better therefrom.

FIG. 8 shows another modified form of relay 120, which can be made extremely small and lends itself very well to present-day electronics applications. Some possibilities are discussed below. The relay comprises four plates 121, 122, 123, and 124, made of glass, ceramic, or .other non-porous, insulating material, and stacked together, as shown in FIG. 8. Two holes and 126 run through all four plates, one hole 127 runs through the' three lowest plates 122, 123, and 124, and one hole 128 runs through the two lowest plates 123 and 124. All the holes are perpendicular to the flat surfaces of the plates. The lower end of the hole 125, which lies in the plate 124, is sealed gas-tight by a metal plug 129 and into the hole 125 is introduced a quantity of transducing agent 130, which is kept in place in the plates 123 and 124 by means of a porous plug 131. Imbedded in the agent 130 is a wire filament 132, one end of which is connected to the metal plug 129. The other end of the filament 132 is connected electrically to a conducting film 133 which lies on the upper surface of the plate 123 and on 'the lower surface of the plate 122 and which extends to the upper end of the hole 128. A metal plug 134 is connected electrically to the film 133 and extends through the hole 128, projecting slightly beyond the lower surface of the plate 124. Thus when a source of current is connected between the metal plugs 129 and 134, the filament is heated and the heat causes the agent 130 to liberate gas. The film 133 extends completely around the hole 125 and seals the joint between plates 122 and' 123 gas-tight. Another film 135 extends around the hole 125 and seals the joint between the plates 123 and 124 gas-tight.

On the wall of the hole 125 between the porous plug 131 and the upper surface of the plate 12,2 is deposited a film 136 of a metal which is wet by mercury. The film 1136 is electric'ally connected to a conducting film 137, which lies on the upper surface of the plate 122 and on the lower surface of the plate 121, and which extends to the upper end of the hole 1127. The film `137 extends completely around Athe hole 1125 and seals the joint between the .plates '121 and 122. A metal plug 138 is connected electrically to the film 137 and extends through the hole V127, projecting slightly beyond the lower sur- -face orf the plate 124. Sealed gas-tight into the upper end of the hole 125 is a contact 139 of metal which is not wet by mercury. The contact 139 extends nearly to the lower surface of the plate 129, leaving-a small gap 140 between the contact and the film v136. The contact 139 is connected electrically to a conducting film 141, which lies on the upper surface of the plate 121 and which extends to the upper end of t-he hole 126. A metal plug 142 is connected electrically to the film 1141 and extends through the hole `126, projecting slightly beyond the lower surface of the plate 124. A small drop 143 of mercury rests in the hole `125, held in place Within the film 136 by capillary attraction. A

The operation of the relay 120 is simple. When a current flows through the filament 132 between the metal plugs 129. and 134 the agent 130 outgasses andl The only change would be an obvious rearrangement of the film 136 and contact 139 to conform to the normallyolosed requirement.

`Clearly the plates 121, 122, 123, and 124 may be made -as large as desired, and many relays of the type shown in `FIG. 8 built in them. These relays may be inter-connected in complex ways by means of conducting films (like the rfilms 133, 137, and 141 in FIG. 8) using printed circuit techniques. In fact, relays of the type shown in FIG. 8 may be made as integr-al parts of printed-circuit boards, with other types of componentsresistors, capacitors, transistors, and so on-mounted thereon and connected by means of conducting lms or printed circuits.

The lform of relay shown in FIG. 8 can be made exeeedingly,small and light weight. The holes may be only a few thousandths of an inch in diameter and the plates may be of the order of 1/16 of an inch thick or less. The presence of a relay in a stack of plates would hardly alter the weight of the plates at all.

The metal film 136 may be deposited in the hole 125 by vacuum evaporation, by chemical deposition, or by electropl-ating. The method chosen depends on the type of metal being deposited. The other films 133, 136, 137, and 141 may be applied by any of the aboive three methods or by spraying or painting. Suitable methods exist in the art for effecting the seals, such `as at the film 135.

Any of the relays shown in FIGS. 1 through S may be changed `from normally open to normally closed, or vice versa, by substituting a type III tran-sducing agent for the type II tranducing agent described. With this change, the transducing agent would ingas upon application o-f current to the filament and would outgas when the filament current is broken.

In any of many methods of heating (llame, sunlight, arc, etc.) the transducing agent 'may be applied to the relays disclosed herein when desired; a filament has been shown throughout this application for Athe sake of simplicity and because of its unique practicality.

In any of the above devices, Class I materials can be used where one-shot operation is desired, The invention enables manufacture of a very reliable and relatively inexpensive relay of this type.

=From the foregoing descriptions it will be apparent that very small relays may be made and that they will be vdependa-ble. External pressures produce no effect on their operation since all contact members are within sealed chambers. Vibration has no effect except possibly in some unusually extreme instance, and even then by proper use of materials, the effect can be eliminated. External magnetic fields have no effect, except as they may be purposely used with induction heating, if desired.

For normal relay operation, it is desirable that the lrelay respond instantly upon application of the actuating current. However, some situations require that the relay not respond until a certain fixed time after application of the lactuating current. From the foregoing discussion it may be seen that a relay utilizing the principles of this invention will respond only when the temperature of its transducing agent reaches a critical value. While instantaneous response can be attained by applying a strong heating to a small mass of transducing agent; nevertheless, if desired, a fixed delay can be introduced lby heating the transducing agent slowly. The length of the time delay can easily be controlled by adjusting the magnitude of the actuating current: the stronger the current, the more rapid the heating of the transducing lagent and lthe shorter lthe time delay. Clearly a time lag could easily be introduced linto the response of any of the above-mentioned forms of this invention merely by reducing the actuating current. All of the factors previously mentioned as affecting the sensitivity of these relays also will affect the time delay characteristics.

While high environmental temperatures can affect the transducing agent, the agent may be chosen to avoid the effect or minimize it. By choosing the right material for the right job, the relay may be used at temperatures far above those where prior-art relays can be used, and the operation will be consistent and dependable.

To those skilled in the art to which this invention relates, many changes in construction and widely differling embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the decription herein are purely illustrative and are not intended lto be in any sense limiting.

I claim:

1. An electrical relay comprising an enclosure; electrically actuated means for generating gas pressure in one end of said enclosure; a capillary tube connected to and forming part of and inside said enclosure beyond said gas generating means; a liquid metal in said tube moved by the variation in pressure in said enclosure, said tube being of a metal that is substantially insoluble in but is wet by said liquid metal; and a pair of electrical contact means bridged by said liquidmetal when it is moved under some pressure conditions and separated by movement of said liquid metal away therefrom under other pressure conditions.

2. The relay of claim 1 wherein said electrically actuated means comprises a metallic hydride.

3. The relay of claim 1 for one-time operation, wherein said electrically actuated means comprises a blowing agent.

4. An electrical relay comprising a sealed enclosure; a solid in said enclosure of the type 'that liberates large quantities of gas as a result of temperature changes, for varying the pressure within said enclosure by'a substantial amount; electrical means for heating said solid above the ambient temperature to vcause the pressure within said enclosure to change markedly from a normal pressure level at said ambient temperature; a capillary tube connected to and forming part of and inside said enclosure and having two portions spaced apart from each other by an insulating portion, said two portions each having a metallic inner surface and each having an electrical connection extending outside said enclosure; and a metal that is liquid at the temperature conditions under which the relay is to be operated so that said metal is moved by pressure changes within said enclosure caused by said electrical means Ito move said metal between a position joining said two portions by bridging said insulating portion and a position separating said two portions, at least one of the metal tube portions being of a metal that is wet by the liquid metal employed and is insoluble therein.

5. The relay of claim 4 wherein said solid is the type the frees its gas when heated.

6. The relay of claim 4 wherein said solid is of the type that absorbs its gas when heated.

7. The relay of claim 4 wherein said capillary tube is separated from said solid by a porous solid retaining plug.

8. The relay of claim 4 wherein both said metal portions are of metal that is wet by the liquid metal employed and is insoluble therein.

9. The relay of claim 4 wherein said capillary tube and its said portions comprise a tube of insulating material having at least two metal tubes snugly fitting therein and spaced apart from each other.

10. The relay of claim 4 wherein said capillary tube and its said portions comprise a tube of insulating material having the metal portions provided by two spacedapart interior thin coatings of metal.

11. An electrical relay comprising a heat-to-pressure transducing solid; means for electrically heating said transducing solid; means defining a tubular insulated passage adjacent to said transducing solid; an electrically conductive capillary tube made of a metal wet by mercury but not dissolved thereby, in said passage; mercury on the inner surface of said capillary tube and moved by a substantial change in pressure caused when said transducing solid is electrically heated; an electrically conductive plug of metal not wet by mercury in said passage spaced from said tube by a gap which is closed by said mercury when said transducing solid is electrically heated; and an electrical circuit including said capillary tube and said plug and closed when they are connected by said mercury.

12. An electrical relay comprising a heat-to-pressure transducing solid; means for electrically heating said solid; means providing a tubular insulated passage adjacent to said transducing solid; an electrically conductive capillary tube, in s aid passage; a liquid metal on the inner surface of said capillary tube and moved by a substantial change in pressure caused when said solid is electrically heated; an electrically conductive plug in said passage spaced from said tube by a gap which is closed by said liquid metal when said solid is electrically heated, said capillary tube being of metal that 4is wet by said liquid metal but insoluble therein, said plug being of metal that said liquid metal does not wet; and an electrical Vcircuit adapted to be connected across said capillary tube and said plug and closed when they are connected by said liquid metal.

13. An electrical relay comprising a heat-to-pressure transducing solid; means for electrically heating said solid; means providing a tubular insulated passage adjacent to said transducing solid; a series of spaced-apart electrically conductive capillary tubes snugly fitting in said passage; and a series of drops of liquid metal on the inner surface of some of said capillary tubes and moved by a substantial change in pressure caused when said solid is electrically heated, each drop bridging from one said tube to another under one kpressure condition, and disconnecting them under another pressure condition, each of said some of said capillary tubes being of metal that is insoluble in said liquid metal and is wet by said liquid metal.

14. An electrical relay comprising a stack of four plates of insulating material, comprising first, second, third, and fourth plates considered serially, said stack having first and second passages extending through all four plates, a third passage extending through said first, second and Athird plates only, and a fourth passage extendt 10 ing through said first and second plates only; a first metal coating on said fourth plate connecting said first and second passages; a second metal coating between said third and fourth plates connecting said first and third passages; a third metal coating between said second and third plates connecting said first and fourth passages; a first metal plug in said first passage in said first plate only and extending out therefrom; a second metal plug in said second passage extending from said rst coating through all said plates and out from said first plate; a third metal plug in said third passage connected to said second coating and therefrom out from said first plate; a fourth metal plug in said fourth passage and connected to said third metal coating and extending out from said first plate; a solid that liberates gas under changes intemperature, in said first passage above said first plug between said first and third plates; an electrical filament through said solid connecting said first plug and said third coating; a fourth coating in said first passage in said third plate and connected to said second coating; a drop of liquid metal in said first passage movable into and out from said fourth coating; and a fifth metal plug closing said first passage at said fourth plate and connected to said first coating and connected electrically to said fourth coating by said liquid metal in one temperature condition and disconnected therefrom at another temperature condition.

References Cited by the Examiner UNITED STATES PATENTS 2,178,487 10/ 1939 Menozzi 200-122 X 2,271,307 1/1942 Ray 73-368 X 2,497,911 2/1950 Reilly et al. 313-178 2,577,653 12/1951 Dysart 200-122 2,627,911 2/ 1953 McCarty et al. 60-25 FOREIGN PATENTS 607,617 9/ 1948 Great Britain. 840,207 7/ 1960 Great Britain.

OTHER REFERENCES Morgan: Plastics Progress, New York Philosophical Library, 1955, pages -58.

BERNARD A. GILHEANY, Primary Examiner. 

1. AN ELECTRICAL RELAY COMPRISING AN ENCLOSURE; ELECTRICALLY ACTUATED MEANS FOR GENERATING GAS PRESSURE IN ONE END OF SAID ENCLOSURE; A CAPILLARY TUBE CONNECTED TO AND FORMING PART OF AND INSIDE SAID ENCLOSURE BEYOND SAID GAS GENERATING MEANS; A LIQUID METAL IN SAID TUBE MOVED BY THE VARIATION IN PRESSURE IN SAID ENCLOSURE, SAID TUBE BEING OF A METAL THAT IS SUBSTANTIALLY INSOLUBLE IN BUT IS WET BY SAID LIQUID METAL; AND A PAIR OF ELECTRICAL CONTACT MEANS BRIDGED BY SAID LIQUID METAL WHEN IT IS MOVED UNDER SOME PRESSURE CONDITIONS AND SEPARATELY BY MOVEMENT OF SAID LIQUID METAL AWAY THEREFROM UNDER OTHER PRESSURE CONDITIONS. 